【codeforces 19/11/06 div2】A. Maximum Square

 1 #include<iostream>
 2 #include<algorithm>
 3 #include<map>
 4 using namespace std;
 5 
 6 map<int, int>cnt;
 7 
 8 int main()
 9 {
10     int T;
11     cin >> T;
12     while (T--)
13     {
14         cnt.clear();
15         int n;
16         cin >> n;
17         for (int i = 1; i <= n; i++)
18         {
19             int t;
20             cin >> t;
21             cnt[t]++;
22         }
23         for (int i = n; i >= 1; i--)
24         {
25             cnt[i] += cnt[i + 1];
26             if (cnt[i] >= i)
27             {
28                 cout << i << endl;
29                 break;
30             }
31         }
32     }
33 }